Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We examine how the qualitative structure of the Doppler peaks in the angular power spectrum of the cosmic microwave anisotropy depends on the fundamental nature of the perturbations which produced them. The formalism of Hu and Sugiyama is extended to treat models with cosmic defects. We discuss how perturbations can be ``active'' or ``passive'' and ``incoherent'' or ``coherent'', and show how causality and scale invariance play rather different roles in these various cases. We find that the existence of secondary Doppler peaks and the rough placing of the primary peak unambiguously reflect these basic properties.

Abstract:

Fluctuations in the cosmic microwave background (CMB) temperature are being studied with ever increasing precision. Two competing types of theories might describe the origins of these fluctuations: ``inflation'' and ``defects''. Here we show how the differences between these two scenarios can give rise to striking signatures in the microwave fluctuations on small scales, assuming a standard recombination history. These should enable high resolution measurements of CMB anisotropies to distinguish between these two broad classes of theories, independent of the precise details of each.

Abstract:

A search is presented for stars that may have formed coevally with the apparently young halo star PHL 346. Candidates were selected for spectroscopy from UBR Schmidt Telescope plates in U.K. Schmidt Telescope survey field 603 scanned with the COSMOS facility at the Royal Observatory, Edinburgh. Spectroscopic observations at ∼ 3.5 Å resolution were made of 72 field stars using the 1.9m telescope at the South African Astronomical Observatory; 16 A- and B-type stars were found, one of which had the appropriate spectral type and radial velocity to be associated with PHL 346. Further photometry and spectroscopy confirmed this identification. The remaining low gravity early-type stars have a mean LSR radial velocity of -75 km s-1, consistent with a non-rotating halo Population.